1. Technical Field
The invention relates to a radio frequency front-end circuit for a receiver and low noise amplifier thereof.
2. Related Art
A radio frequency (RF) front-end circuit for receiver is mainly applied in a communication system, which amplifies a signal received from an antenna to facilitate signal process. Since the signal comes from the antenna is very weak, the RF front-end circuit is generally closed to the antenna to minimize a signal loss on the transmission line. Such configuration is widely used in receiver of a wireless communication system, etc., for example, a wireless local area network (WLAN) or a global positioning system (GPS), etc. In some real applications, a low noise amplifier applied in the receiver is followed by a quadrature passive mixer, which mixes and converts the RF signal received from the antenna into a baseband signal then pass to next stage. According to the existing technique, the quadrature passive mixer followed by the low noise amplifier shares the differential RF signal from the low noise amplifier output, and converts the differential RF signal into a differential in-phase baseband signal and a differential quadrature-phase baseband signal. However, a 25% duty cycle local oscillation generator has to be used to avoid the signal and noise interfering between in-phase channel and quadrature-phase channel, so as to avoid the degradation of signal to noise ratio.